Mine hoop pins and apparatus for setting the same

ABSTRACT

1. A ROOF PIN ADAPTED TO BE PRESSED INTO A MINE ROOF, COMPRISING: (A) ELONGATE SHANK MEANS HAVING A HEAD AT ONE END AND A POINTED TIP AT THE OTHER END, A FIRST PORTION OF THE SHANK MEANS BEING OF GREATER PERIPHERAL DIMENSION THAN A SECOND PORTION TO PROVIDE A CONTACT SURFACE ENGAGEABLE WITH THE ROOF MATERIAL WHEN THE PIN IS PRESSED INTO THE MINE ROOF, THE AREA OF THE CONTACT SURFACE BEING PRESELECTED TO CONTROL THE AMOUNT OF SURFACE PRESSURE AND SKIN FRICTION AND THEREBY PREDETERMINE THE FORCE REQUIRED FOR INSERTION. (B) THE FIRST SHANK PORTION, THAT IS OF GREATER PERIPHERAL DIMENSION AND PROVIDES THE PRESELECTED CONTACT SURFACE AREA, IS LOCATED AHEAD OF THE RELATIVELY REDUCED SECOND SHANK PORTION IN THE DIRECTION OF THE POINT TIP TO PROVIDE A PASSAGE IN THE ROOF STRATA THAT IS LARGER THAN THE REDUCED SHANK PORTION.

s. w. ELDERS Re. 28, 227

Nov. 5, 1914 M1! ROOF PINS AND APPARATUS FOR SETTING THE SAME OriginalFiled Jan. 2, 1970 2 SheetsSheet 1 fig G. w. ELDERS Re. 28, 227

Nov. 5, I974 MINE ROOF PINS AND APPARATUS FOR SETTING THE SAME OriginalFiled Jan. 2, 1970 2 Sheets-Sheet 2 5 5 M Z w l 7 4 M a 5 w 5% WWW k NT1} 0 United States Patent 28,227 MINE ROOF PINS AND APPARATUS FORSETTING THE SAME Gerald W. Elders, Aspen, Colo., assignor to Lee-NorseCompany, Charleroi, Pa.

Original No. 3,643,542, dated Feb. 22, 1972, Ser. No. 110, Jan. 2, 1970,which is a continuation-impart of application Ser. No. 846,795, Aug. 1,1969. Application for reissue Apr. 18, 1973, Ser. No. 352,278

Int. Cl. F16b /00 U.S. C]. 8510 R 9 Claims Matter enclosed in heavybrackets I] appears in the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade by reissue.

ABSTRACT OF THE DISCLOSURE A roof pin adapted to be pressed into a mineroof which includes an elongate shank having a head at one end and apointed tip at the other end, a first portion of the shank being ofgreater peripheral dimension than a second portion to control the amountof surface pressure and skin friction when pressed into the mine roof,and thereby predetermine the force required for insertion. The relativelongitudinally axial length of the first and second shank portions arepreselected to provide such regulation. In one embodiment, the firstshank portion is located ahead of the relatively reduced second shankportion in the direction of the pointed tip to provide a passage in theroof strata that is larger than the reduced second shank portion.

The method of installing a pin of this type in a mine roof comprises thesteps of inserting the elongate pin by pressing into the mine roof,subjecting the mine roof to a compressive pressure in the area of thepin to force the strata tightly together so that the pin will hold thestrata in such condition, and releasing the compressive pressure afterthe pin has been inserted so that the roof strata will providesubstantially full length contact with the pin to lock the pin in place.In those pins in which the first shank portion is located ahead of therelatively reduced second shank portion in the direction of the pointedtip, the roof strata will fill in behind the first shank portion andassist in locking the pin in place when the compressive pressure isreleased after the pin has been inserted.

The pin-setting device for use in fixing pins of this type in a mineroof include positioning means that locate the pin at a predeterminedarea of the roof and subject the mine roof to the compressive pressurein the predetermined area to force the roof strata tightly together sothat the pin will hold the strata in such condition, and which willselectively release the compressive pressure after the pin has beeninserted so that the roof strata will provide substantially the fulllength contact with the pin to lock the pin in place.

CROSS REFERENCE TO RELATED APPLICATION This application is acontinuation-in-part of copending application Ser. No. 846,795, filedAug. 1, 1969 and entitled Apparatus for and Method of Setting Pins inMine Roofs.

BACKGROUND OF THE INVENTION This invention relates generally toimprovements in roof bolting for mines, and more particularly toimproved pins and apparatus for and method of setting pins in mineroofs.

In the heretofore conventional method of installing roof bolts in mineroofs, a hole approximately 1% inches in diameter was drilled in theroof and was adapted to Reissued Nov. 5, 1974 receive a /s inch bolt andexpansion shell. The expansion shell was located on the bolt andinserted into the drilled hole, the bolt being turned to expand theshell into gripping engagement With the hole wall. The hole was drilledto a depth until a a solid roof strata was reached and the expansionshell was anchored in this roof strata. It will be understood that theroof was hung from this bolt. There were essentially two separateoperations in installing the bolt, namely, (1) drilling the hole, and(2) installing the bolt and shell in the hole and tightening the boltunder torque. The expansion shell represented the only bearing areaholding the bolt in the roof.

In many instances, there are areas in a mine in which there is nosufficiently rigid roof strata in which to anchor an expansion shell.This type of installation was not successful in those areas. Moreover,in many instances, sulficient anchorage strength was not achievedbecause support was limited by the amount of bearing area presented bythe expansion shell. The bolt does not contact the roof material.Tightening the bolt upon application of torque does not increase theholding power because it is limited by the type of material engaging theexpansion shell.

The drilling of the hole in the mine roof has a tendency to relieve anycompressive pressures inherent between the roof strata. Roof jacks areused only when the roof condition presents a hazard to the well-being ofthe miners and used to keep the rock from falling. At the present time,the greatest source of injury in a mine is caused by rock falling fromthe roof. In addition, a further health hazard is created by a drillingof such roof holes, in that the dust is particularly harmful to thelungs and eyes of miners.

In other fields of endeavor, pins have been driven into walls by hammersthat apply a series of abrupt impact shock blows to the pins. Thismanner of driving pins is undesirable in mines because the impact tendsto disturb the otherwise stable condition of the roof strata, not onlyin the immediate area in which the pin is driven, but for a considerabledistance in all directions, and can adversely affect the holding powerof previously driven pins.

The apparatus for and method of setting pins in mine roofs, disclosed inthe copending US application mentioned previously, eliminates the needfor drilling any holes in the roof and eliminates any dust hazard thatheretofore has been injurious to the miners, and avoids the relief ofroof pressure. Moreover, the need for driving the pin by hammer blows isalso eliminated, thereby avoiding the undesirable and potentiallydangerous conditions that are caused by such impact shock. The pin ispressed into the mine roof with a substantially smooth force whichavoids any chipping or removal or shock disturbance of roof material.The full length of the pin contacts the material of the mine roof forgreater holding power and is not limited merely by the bearing surfaceprovided by an expansion shell. Because the pin is pushed into the mineroof upon installation, there is no torque applied to the pin. It is notnecessary to find a limestone roof strata in order to provide aneffective installation of the pin when placed in position. The pin, whenpushed into the mine roof creates a wedging formation of the materialperipherally around and engaging the pin, whereby to enhance the holdingpower of the pin.

As each pin is pressed into the mine roof, a compressive pressure isexerted on the roof in the area in which the pin is located in order toforce the roof strata tightly together and so that the pin will hold thestrata in such a condition. Such compressive pressure can be applied tothe roof before insertion of the pin and/or during insertion and/orafter insertion by pressure applied to the pm.

The pin-setting device used in fixing the pins in the mine roof includesan elongate cylinder having an openend and a closed-end, and a pistonmovably mounted in the cylinder. A positioning means locates the openend of the cylinder at the predetermined area of the roof, and meansintroduces fluid into the cylinder one side of the piston to move thepiston and to press the pin located in the cylinder into the mine roofunder a substantially smooth pushing force. The positioning meanssubjects the mine roof to the compressive pressure in the predeterminedarea to force the roof strata tightly together so that the pin will holdthe strata in such condition. This compressive pressure can be appliedby jacks extending between the mine roof and floor.

Under some circumstances, it has been found that roof pins having aconstant shank diameter and over 20 inches in length required a greatdeal of compressive force to press the pin completely into the roofstrata. The use of such large compressive forces are not practical insome mines depending upon the space available and the condition of theroof and floor.

SUMMARY OF THE INVENTION The improved roof pins are especially designedto require less compressive force to press the pins completely into theroof strata. For example, instead of requiring a force of substantiallyseventy (70) tons to press a thirty inch roof pin into the mine roof,the pin is constructed so that only a force of substantially forty (40)tons is required and yet maintains standards that far exceed those setby the United States Bureau of Mines in prescribing what is acceptableas a good pull test. According to the standards set by the United StatesBureau of Mines, a 6000 pound pull is accepted as a good result on aroof bolt. With the present pin, method and apparatus for installingsuch pins, the pins have withstood at least 12,000 pounds of pullwithout any sign of disturbance.

The roof pin adapted to be pressed into the mine roof includes anelongate shank having a head at one end and a pointed tip at the otherend, a first portion of the shank being of greater peripheral dimensionthan a second shank portion to control the amount of surface pressureand skin friction when pressed into the mine roof and therebypredetermine the force required for insertion. The relativelongitudinally axial lengths of the first and second shank portions areselected to provide a controlled amount of surface pressure and skinfriction on the pin to regulate the insertion force required.

In one embodiment, the first shank portion of the roof pin that is ofgreater peripheral dimension, is located ahead of the relatively reducedsecond shank portion in the direction of the pointed tip to provide apassage in the roof strata that is larger than the reduced second shankportion. The enlarged first shank portion can be a peripheral ringlocated near the pointed tip or a plurality of relatively smallprotuberances on the shank near the pointed tip [or a substantiallyhelical rib located substantially at the pointed tip] or a substantiallyhelical rib located substantially at the pointed tip.

The method of installing a pin of. the type previously described in amine roof comprises the steps of inserting the elongate pin by pressingit into the mine roof, subjecting the mine roof to a compressivepressure in the area of the pin to force the strata tightly together sothat the pin will hold the strata in such condition, and releasing thecompressive pressure after the pin has been inserted so that the roofstrata will provide substantially full length contact with the pin tolock the pin in place. When using a pin in which a first shank portionis located ahead of the relatively reduced second shank portion, thefirst shank portion provides a passage in the roof strata that is largerthan the reduced second shank portion. The roof strata will fill inbehind the enlarged first shank portion and assist in locking the pin inplace when the compressive pressure is released after the pin has beeninserted.

Ill

Ill)

4 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view,partly in cross section, as taken in a vertical center plane passedthrough a pin-setting device and illustrating one pin embodiment;

FIG. 2 is a fragmentary, side elevational view of another pinembodiment;

FIG. 3 is a fragmentary, side elevational view of another pinembodiment;

FIG. 4 is a fragmentary, side elevational view, partly in cross section,of another pin embodiment;

FIG. 5 is a side elevational view of a split collar utilized in the pinembodiment of FIG. 4;

FIG. 6 is a top plan view of the split collar of FIG. 5;

FIG. 7 is a fragmentary, side elevational view of another pinembodiment;

FIG. 8 is a fragmentary, side elevational view of another pinembodiment;

FIG. 9 is a top plan view of the pin shown in FIG. 7, and

FIG. 10 is a fragmentary, side elevational view of another pinembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now by characters ofreference to the drawings and first to FIG. I, it will be understoodthat the pin-setting device generally indicated by 10 is located andextends between a mine roof 11 and the subjacent mine floor 12.

The pin-setting device 10 includes an elongate pin cylinder 13 having anopen-end 14 and a closed-end 15. A cylinder port 16 communicates withthe cylinder 13 near the closed bottom end and communicates with a fluidmeans such as a hydraulic pump (not shown). An air port 17 is providedin the cylinder 13 adjacent the open-end 14 to provide for the freepassage of air.

Located and slidably mounted in the cylinder 13 is a piston referred toby 20, the piston 20 consisting of two interconnected, yet separableupper and lower parts. Formed in the upper side of piston 20 is adownwardly tapered socket 21 that forms a pin seat. The concaveconfiguration of the upper piston side assists in seating the pin headand in clearing dust from the cylinder wall. As is conventional, thepiston 20 carries a plurality of piston rings 22 that provide anefiective seal between the piston 20 and the wall of pin cylinder 13.The lower side of piston 20 is divergent upwardly so as to provide aclearance with the cylinder port 16, whereby fluid such as oil can passtherethrough even when the piston 20 is located in its lowermostlocation in the cylinder 13.

Attached to and carried by the lower closed end 15 of pin cylinder 13,is a mounting plate 23, the mounting plate 23 extending laterallyoutward from cylinder 13. Provided in the mounting plate 23 at oppositesides of the pin cylinder 13, are a pair of holes 24.

A positioning means is carried by the pin cylinder 13 for locating theopen cylinder end 14 at a predetermined area of the mine roof 11. Thispositioning means includes a pair of hydraulic jacks referred to bylocated at op posite sides of the pin cylinder 13. Each hydraulic jack[24] 25 includes an elongate cylinder 26 having its upper end engagingand closed by a pressure plate 27 that is fixed to the pin cylinder 13at the upper open cylinder end 14. Reciprocatively mounted in each jackcylinder 26 is a piston 30 to which an elongate piston rod 31 isattached. The piston rod 31 extends through the closed bottom end ofjack cylinder 26 and through the aligned hole 24 formed in the mountingplate 23. The piston rods 31 are provided with feet 32 that seat on themine floor 12. Each jack cylinder 26 is provided with a hydraulic port33 at its bottom end and a hydraulic port 34 at its upper end, thehydraulic ports 33 and 34 communicating with the jack cylinder 26 atopposite sides of the piston 30.

When used, the hydraulic jacks are retracted and the pin-setting deviceis disposed in a substantially upright position with the jack feet 32seating on the mine floor 12. A wood block 35 is disposed on top of thepressure plate 27 and overlapping the open cylinder end 14. Uponextension of the hydraulic jacks 26, the pressure plate 27 will urge theWood block 35 against the mine roof 11 and will clamp the block 35 inplace at the predetermined area.

A safety means generally indicated by [37] 36 is carried by the pincylinder 13, and is particularly mounted to one of the hydraulic jackcylinders 26. This safety means 36 includes a switch that is operativelyconnected to the hydraulic system so as to prevent operation of thehydraulic system unless the switch is actuated. The switch is actuatedby an elongate plunger 37 that extends upwardly through the pressureplate 27 and into an engagement with the wood block 35. When thepin-setting device is located in its operable position, the plunger 37is depressed a predetermined distance so as to actuate the switch of thesafety means 36, and thereby conditions the hydraulic system foroperation.

The pin referred to by 40 in FIG. 1 that is to be driven by thepin-setting device into the mine roof 11, includes an elongate shank 41having a head 42 at one end and a pointed tip 43 at the other end. Itwill be understood that a first portion 44 of the shank 41 is of greaterperipheral dimension than a second portion 45 to control the amount ofsurface pressure and skin friction when pressed into the mine roof, andthereby predetermine the force required for insertion. The relativelongitudinally axial lengths of the first and second shank portions 44-and 45 respectively are selected to provide such force regulation. Inthe roof pin 40, the first shank portion 44, that is of greaterperipheral dimension, is located ahead of the relatively reduced secondshank portion 45 in the direction of the pointed tip 43 to provide apassage in the roof strata that is larger than the reduced second shankportion 45.

Mounted on and carried by the elongate pin shank 40 are one or morediscs 46. These discs 46 are press-fitted on the pin shank 41 so thatthey will maintain their original axial displacement as the pin 40 ishandled prior to being pressed into the mine roof 11. However, thisconnection between the discs 46 and the pin shank 41 will enable thediscs 46 to slide longitudinally along the pin shank 41 as each discengages the block 35, constituting an abutment, as the pin 40 is pressedinto place. When the pin 40 is fully installed, the discs 46 will beclamped between the pin head 42 and the wood block 35 to provide asubstantially solid bearing plate. The discs 46 retained the pin 40 inits centered position within the pin cylinder 13 and guide the pin 40 inits movement along the cylinder 13.

Another pin embodiment is disclosed in FIG. 4. In this embodiment, thepin 47 includes an elongate shank 50 having a head 51 at one end and apointed tip 52 at the other end. Similar to the construction of pin 40in FIG. 1, the pin 47 in FIG. 4 has as its first shank portion 53 aheadof the relatively reduced second shank portion 54 in the direction ofthe pointed tip 52. Fitted on and retained by the elongate shank 50 is asplit collar 55, the collar 55 having an internal, upwardly divergentcamming surface 56 that engages a compatible and coacting cammingsurface 57 formed on the first shank portion 53. As is preferred, theperipheral dimension of the collar 55 is substantially the same as thatof the first shank portion 53 so as to provide a substantially flushoutermost surface. When the pin 47 is pressed into the mine roof, thefirst shank portion 53 including the collar 55 will provide a passage inthe roof strata that is larger than the second shank portion 54. Whenfully inserted, and a pull is inserted on the pin 47, the surfacepressure exerted on the split collar 55 will cause the collar to ride upon the camming surface 57, thereby causing an expansion of the collar 55to increase the holding power of the pin 47.

Another pin embodiment is shown in FIG. 2. In this embodiment, the pin60 includes an elongate shank 61 having a head 62 at one end and apointed tip 63 at the opposite end. The shank 61 has a first shankportion 64, that is of greater peripheral dimension, located behind therelatively reduced second shank portion 65 in the direction of thepointed tip 63.

Another pin embodiment is disclosed in FIG. 3. In this embodiment, thepin 66 includes an elongate shank 67 having a head 70 and a pointed tip71 at the other end. The enlarged shank portion 72 is a peripheral ringlocated near the pointed tip and having the greater peripheral dimensionthan the relatively reduced second shank portion 73 located behind thering, the ring being slightly tapered.

Another roof pin embodiment is disclosed in FIG. 7. In this embodiment,the roof pin 74 includes a shank 75 having a head 76 at one end and apointed tip 77 at the other end. The first shank portion 80 includes aplurality of relatively small protuberances 80 located on the shank 75near the pointed tip 77. These protuberances 80 are preferably locatedon the pointed tip 77 but clear of the terminal tip end. The relativelyreduced second shank portion 81 is located behind the first shankportion 80. The protuberances are located in a random or predeterminedpattern around the circumference of the shank 75 and will provide apassage in the roof's strata that is larger than the second shankportion 81 when the pin 74 is pressed into the mine roof 1].

Another pin embodiment is disclosed in FIGS. 8 and 9. In thisembodiment, the pin 82 is similar in construction to pin 40 previouslydescribed in that the pin 82 includes an elongate shank 83 having afirst shank portion 84 that is of greater peripheral dimension than asecond shank portion 85, the enlarged first shank portion being locatedahead of the second shank portion 85. The first shank portion 84 isprovided with a plurality of longitudinal, peripherally spaced grooves86 that are open at both ends of the first shank portion 84 for thepassage of roof material and to further control the amount of surfacepressure and skin friction. These grooves 86 are substantially straightand parallel to the longitudinal axis of the shank 83. The first shankportion includes a part of the pointed tip 87. The grooves 86 extend onthe pointed tip 87 but terminate short of the outermost tip end. A head88 is provided on the opposite shank end.

Another pin embodiment is disclosed in FIG. 10. In this embodiment, theroof pin 90 includes an elongate shank 91 having a head 92 at one endand a pointed tip 93 at the other end. The first shank portion 94 is asubstantially helical rib located substantially at the pointed tip 93.The helical rib can be of substantially one turn on the pin shank 91 orit can be of more than one turn. The first shank portion 94 provided bythe rib has a greater peripheral dimension that the relatively reducedshank portion 95 and is located ahead of the second shank portion 95 soas to provide a passage in the roof strata that is larger than theperipheral dimension of the second shank portion 95. To provide a leadin for the relatively enlarged first shank portion 94, the helical ribextends at least partially on the pointed tip 93.

The method of installing a pin of the type previously described into amine roof comprises the steps of inserting the elongate pin by pressinginto the mine roof, subjecting the mine roof to a compressive pressurein the area of the pin to force the strata tightly together so that thepin will hold the strata in such condition, and releasing thecompressive pressure after the pin has been inserted so that the roofstrata will provide substantially full length contact with the pin shankto lock the pin in place. With those pins in which the first shankportion of greater peripheral dimension than the second shank portion islocated ahead of the relatively reduced second shank portion, the actionof pressing the pin into the mine roof provides a passage in the roofstrata that is larger than the reduced shank portion. When thecompressive pressure on the mine roof is released after the pin has beeninserted, the roof strata will fill in behind the first shank portionand assist in locking the pin in place.

The pin-setting device adapted for use in fixing the pins in the mineroof includes means for pressing the pin into the mine roof, andpositioning means that locates the pin at a predetermined area of theroof and subjects the mine roof to a compressive pressure in thepredetermined area to force the roof strata tightly together so that thepin will hold the strata in such condition. The positioning meansselectively releases the compressive pressure after the pin has beeninserted so that the roof strata will provide substantially full lengthcontact with the pin to lock the pin in place.

It is thought that the operation of the pin-setting device 10 has becomefully apparent from the foregoing detailed description of parts, but forcompleteness of disclosure, the method of usage will be brieflydescribed.

First, it will be assumed that the jacks 25 are fully retracted, andthat the pin piston is dropped to its lowermost position. The pin, forexample pin 40 in FIG. 1, is then placed into the cylinder 13 throughthe open end 14 so that the pin head 42 seats in the piston socket 21.

The pin discs 46 will engage the cylindrical wall and guide i pin 40 toits appropriate centered position. When the pin 40 is placed in thecylinder 13 and seated on the piston 20, the pointed tip 43 will belocated within the open cylinder end 14. Then, the wood block 35 isplaced on top of the pressure plate 27, overlapping the open cylinderend 14. The pin-setting device 10 is located in its substan tiallyvertical position, with the jack feet 32 seating on the mine floor 12.and the jacks are extended to clamp the block 35 against the mine roof11 at the predetermined area at which the pin is to be fixed.

A compressive pressure is applied to the mine roof 11 by the actuationof the jacks 25, the compressive pressure being applied through thepressure plate 27 and the wood block 35. This compressive pressure inthe area at which the pin is to be fixed, forces the roof strata tightlytogether and preconditions the roof for the reception of the pin 40.While this compressive pressure is being applied to the mine roof 11,the pin 40 is pressed into the mine roof 11 by a substantially smoothpushing force applied to the pin head 42 through the piston 20. As thepin 40 is L pushed, preferably with a smooth pushing force, the pin 40will first pierce the block 35 and then move into the mine roof 11. Asthe pin 40 penetrates the roof strata, there is a full bearing contactof the roof material with the first shank portion 44. Upon continuedpenetration, the first shank portion 44 will provide a passage in theroof strata that is slightly larger than the relatively reduced shankportion 45. Predetermining the bearing contact area of the shank portion45 and skin friction, and thereby determine the amount of force requiredto complete the insertion. Moreover, the inward movement of the pin 40will cause the loose strata to deform slightly in the direction of thepenetration in the immediate area contacting the roof pin 40, therebycreating a wedge formation that further increases the holding power ofthe pin 40.

As the pin 40 is pushed into the mine roof 11, the discs 46 will guidethe movement of pin 40 axially along the pin cylinder 13. The uppermostdisc 46 will first engage the underside of the block 35 at the opencylinder end 14. and will then slide relatively longitudinally along thepin shank 41. The next disc 46 will then engage the first disc 46 whenit reaches the open cylinder end 14 and will effectively abut the block35, and then such disc 46 will move slidabiy, longitudinally along thepin shank 41 in a direction toward the pin head 42. When fully pressedinto place, the discs 46 are clamped between the pin head 42 and theblock 35.

It is desirable to place a further compressive pressure on the roofstrata of the mine roof 11 by pushing the pin head 42 with the pinpiston 20, this compressive pressure being applied to the disc 46constituting the bearing plate, and the block 40. This additionalcompressive pressure further conditions the roof strata by forcing thestrata even more tightly together. The pin 40 will then hold the roofstrata in such condition.

After the pin 40 has been installed, the pin piston 20 is retracted byrelieving the hydraulic pressure. Then, the jacks 25 are retracted. Therelease of the compressive pressure causes a very slight relaxation ofthe roof strata that permits the strata to fill in behind the firstshank portion 44 of the pin 40 and thereby provide substantially fulllength contact with the pin to lock the pin securely in place.

With those pins 40, 47, 66, 74, 82 and in which the relatively enlargedfirst shank portion is located ahead of the remaining second shankportion, it is at times desirable to reduce the peripheral dimension ofthe second shank portion to such an extent that the roof material doesnot effectively contact the second shank portion after the pin iscompletely pressed into place so as to enhance the pulling forcerequirements. Under these circumstances, the length of the enlargedfirst shank portion will determine both the amount of force required forinsertion and also the pulling force requirement. It will be understoodthat if it is determined that say a ten (l0) inch length of enlargedfirst shank portion will far exceed the pull force standards of theBureau of Mines and permit insertion under reasonable pushing force, therelatively reduced second shank portion, and hence the overall pin, canbe of any desired length.

I claim as my invention:

1. A roof pin adapted to be pressed into a mine roof, comprising:

(a) elongate shank means having a head at one end and a pointed tip atthe other end, a first portion of the shank means being of greaterperipheral dimension than a second portion to provide a contact surfaceengageable with the roof material when the pin is pressed into the mineroof, the area of the contact surface being preselected to control theamount of surface pressure and skin friction and thereby predeterminethe force required for insertion.

(b) the first shank portion, that is of greater peripheral dimension andprovides the preselected contact surface area, is located ahead of therelatively reduced second shank portion in the direction of the pointedtip to provide a passage in the roof strata that is larger than thereduced shank portion.

2. A roof pin as defined in claim 1 in which:

(0) the area of the contact surface has a longitudinally axial lengthpreselected to provide the controlled amount of surface pressure andskin friction on the pin to regulate the insertion force required.

3. A roof pin as defined in claim 2, in which:

(d) the first shank portion is substantially cylindrical and of greaterdiameter than the second shank portion and is located ahead of thesecond shank portion in the direction of the pointed tip to provide apassage in the roof strata that is larger than the second shank portion,the preselected area of the contact surface being provided by thecylindrical peripheral surface of the first shank portion.

4. A roof pin as defined in claim 2, in which:

(d) the first shank portion is a peripheral ring located near thepointed tip, the preselected area of the contact surface being providedby the peripheral ring and the tapered periphery between the tip and thering.

5. A roof pin as defined in claim 2, in which:

(d) the first shank portion includes a plurality of relatively smallprotuberances on the shank means near the pointed tip, the preselectedarea of the contact surface being provided by the protubcrances.

6. A roof pin as defined in claim 2, in which:

((1) the first shank portion includes a plurality of iongitudinal,peripherally spaced grooves that are open at both ends of the firstshank portion for the passage of roof material and to further controlthe amount of surface pressure and skin friction, the

friction and thereby predetermine the force required for insertion,

(h) the first shank portion, that is of greater peripheral dimension andprovides the preselected contact surface, is located ahead of therelatively reduced second shank portion in the direction of said endadapted to enter the roof to provide a passage in the roof strata thatis larger than the reduced shank portion.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original the firstshank portion is provided with a plurality patent. of longitudinal,peripherally spaced grooves that are UNITED STATES PATENTS open at bothends of the first shank portion for the 1 200 594 10/191 Curtis 85 21passage of roof material and to further control the 1,332,059 2/1920 N d35 21 amount of surface pressure and skin friction. the 1,360,34411/1920 Wood et a], 85 3() X reselected area of the contact surfacebeing pro- 1,972,119 9/1934 Wernhardt 85-21 vided by the peripherybetween the grooves. 2,207,897 7/1940 Schaus 85-10 X 8. A roof pin asdefined in claim 2, in which: 2,203,294 6/1940 Eagle 85 10 (d) the firstshank portion is a substantially helical 2,095,153 10/1937 Rosenberg 5-rib located substantially at the pointed tip, the pre- 2,356,375 3/1944Brown 8519 selected area of the contact surface being provided 2,504,3114/1950 Dunn 85l0 E UX by ennmg e a. with; r t p adapted to be Pressed mma f, will 3,091,991 6/1963 Baker 85 44 X (a) elongate shank means havingan end adapted to FOREIGN PATENTS enter the roof, :1 first portion ofthe shank means 782,804 4/1968 Canada 85 10 E being of greaterperipheral dimension than a second portion to provide a Contact surfaceert gageable with the roof material when the pin is pressed into theroof, the area of the Contact surface being preselected to control theamount of surface pressure and skin DENNIS L. TAYLOR, Primary ExaminerUS. Cl. X.R. 6145 B; 30

